All,


I recently purchased a second hand (but new-in-box) nifty fifty. After taking some shots around the house and outside, I was beginning to question it's autofocus. So I setup up an impromptu focus test. I used a tripod and cable release taking a picture of a magazine article on the ground at about a 45 degree angle (3-4 feet from the lens). I had the camera set on Av Priority at f/1.8, ISO 100. Most of the pictures were 1/40 sec, a few were 1/30.


After each photo, I reset the focus to infinity to make the lens search for focus. I took 6 photos with the center focus point, 3 photos with the far left point, and 3 photos with the far right point. BTW, I have a 50D.


To summarize, the focus was all over the place. In case I am mixing up the terminology, when I say it front-focuses I mean it is focusing on the paper closer to the camera than where I want; and the opposite for back-focusing. For the 6 center focus point shots; I had 3 back-focused, 2 front-focused, and one dead-on. For the 3 left focus point shots; I had 2 dead-on and 1 front-focused. For the 3 right focus point shots; all 3 were back-focused.


If my test is flawed, please let me know what I need to do different for a more accurate test. Otherwise, what's going on with my lens?


Thanks,


Braden